DESCRIPTION: (Applicant's Abstract) Chronic lymphocytic leukemia (CLL), the most common form of leukemia in North America and Europe, accounts for more than 30 percent of all cases. CLL is characterized by the accumulation of non-dividing CD5+ B cells in GO of the cell cycle. This is currently an incurable malignancy; there is a great need for new insights into disease mechanisms. Nitric oxide (NO) is produced in vivo from L-arginine by the enzyme NO synthase (NOS). NO has multiple actions that play important roles in physiology and pathology. Recent work has demonstrated that NO inhibits apoptosis. We have discovered that human CLL cells spontaneously express high levels of inducible nitric oxide synthase (NOS2) mRNA and protein, and have high NOS enzyme activity. When the CLL cells are cultured with NOS inhibitors, there is high level cell killing associated with apoptosis. The specific aims of the proposal are to: (1) Determine if in vivo NO production is increased in patients with CLL, and whether in vivo NO production correlates with NOS2 expression in CLL cells, stage of disease, and subsets of disease. We will measure serum and urine levels of the stable NO catabolites nitrite and nitrate in patients with CLL, and correlate levels with CLL cell NOS activity & NOS2 antigen content and clinical stage of disease. (2) Determine the sensitivity of patients' CLL cells to a variety of NOS inhibitors and NO quenchers. We will analyze CLL cells in vitro for viability and apoptosis after treatment with selected NOS (NOS2 specific and nonspecific) inhibitors and NO quenchers. We will also investigate the effects of combining NOS inhibitors & NO quenchers with conventional chemotherapeutic agents. (3) Determine the mechanism by which NOS2 expression is increased in CLL cells. We will determine whether the increases in NOS2 mRNA expression are due to alterations in mRNA transcription or stabilization, and whether there is constitutive activation of transcription factors known to alter NOS2 mRNA transcription. NOS2 and NO represent new molecular targets for treatment in CLL, Accomplishment of the proposed aims may provide a deeper understanding of the mechanisms of disease in CLL. Furthermore, since NOS inhibitors and NO quenchers/scavengers are now being used safely in early trials in normal volunteers and in patients with other diseases, our work may lead to rapid initiation of trials with these agents in CLL patients.